With respect to the production method of tetramethylammonium methyltriphenylborate as one of borate compounds represented by formula (1) shown later, a method of ion-exchanging lithium methyltriphenylborate obtained from triphenylborane and methyllithium by tetramethylammonium bromide is commonly known [see, for example, Journal of American Chemical Society, Vol. 107, pp. 6710-6711 (1985)].
With respect to the production method of triphenylborane, a method of reacting metallic magnesium, boron trifluoride diethyl etherate and phenyl bromide in diethyl ether is commonly known [see, for example, Journal of Organic Chemistry, Vol. 51, pp. 427-432 (1986)].
More specifically, in the case of the tetramethylammonium methyltriphenylborate, phenyl bromide is reacted with metallic magnesium in diethyl ether to prepare a Grignard reagent, the reagent is added dropwise to a solution containing boron trifluoride diethyl etherate dissolved in diethyl ether, the mixed solution is stirred for several hours to obtain triphenylborane, the triphenylborane obtained is added to methyllithium without passing through isolation to form lithium methyltriphenylborate, and tetramethylammonium bromide is added thereto to effect ion exchanging, as a result, tetramethylammonium methyltriphenylborate is obtained.
With respect to the production method of alkyldiaryl boronate (or aryldialkyl boronate), a method of reacting a boric acid ester with a Grignard reagent or organic lithium in diethyl ether is commonly known [see, for example, Organometallics, pp. 1058-1067 (1993)].
In these conventional production methods, the solvent used for the Grignard reaction or reaction of triarylborane or trialkylborane is restricted to diethyl ether in view of the problem of side reaction [see, for example, Journal of Organic Chemistry, Vol. 51, pp. 427-432 (1986)].
The Grignard reaction in general is, however, easy to occur in tetrahydrofuran rather than in diethyl ether [see, for example, Teruaki Mukaiyama (compiler), Kiso Yuki Kagaku (Basic Organic Chemistry), Maruzen, page 79] and in the case of halides difficult to cause the Grignard reaction in diethyl ether, the final yield of the borate compound disadvantageously decreases.